研究者データベース

大場 康弘(オオバ ヤスヒロ)
低温科学研究所 共同研究推進部
准教授

基本情報

所属

  • 低温科学研究所 共同研究推進部

職名

  • 准教授

学位

  • 博士(理学)(岡山大学)

ホームページURL

J-Global ID

研究分野

  • 自然科学一般 / 宇宙惑星科学

職歴

  • 2020年12月 - 現在 北海道大学低温科学研究所 准教授
  • 2015年04月 - 2020年11月 北海道大学 低温科学研究所 助教
  • 2012年04月 - 2015年03月 北海道大学 低温科学研究所 特任助教
  • 2009年04月 - 2012年03月 日本学術振興会特別研究員(PD)
  • 2008年04月 - 2009年03月 北海道大学低温科学研究所 博士研究員
  • 2007年04月 - 2008年03月 University of Nevada-Reno (USA) 博士研究員

研究活動情報

論文

  • Yasuhiro Oba, Yoshinori Takano, Yoshihiro Furukawa, Toshiki Koga, Daniel P. Glavin, Jason P. Dworkin, Hiroshi Naraoka
    Nature Communications 13 1 2022年12月 
    Abstract The lack of pyrimidine diversity in meteorites remains a mystery since prebiotic chemical models and laboratory experiments have predicted that these compounds can also be produced from chemical precursors found in meteorites. Here we report the detection of nucleobases in three carbonaceous meteorites using state-of-the-art analytical techniques optimized for small-scale quantification of nucleobases down to the range of parts per trillion (ppt). In addition to previously detected purine nucleobases in meteorites such as guanine and adenine, we identify various pyrimidine nucleobases such as cytosine, uracil, and thymine, and their structural isomers such as isocytosine, imidazole-4-carboxylic acid, and 6-methyluracil, respectively. Given the similarity in the molecular distribution of pyrimidines in meteorites and those in photon-processed interstellar ice analogues, some of these derivatives could have been generated by photochemical reactions prevailing in the interstellar medium and later incorporated into asteroids during solar system formation. This study demonstrates that a diversity of meteoritic nucleobases could serve as building blocks of DNA and RNA on the early Earth.
  • Kenji Furuya, Tetsuya Hama, Yasuhiro Oba, Akira Kouchi, Naoki Watanabe, Yuri Aikawa
    The Astrophysical Journal Letters 2022年07月01日
  • Muneaki Imai, Yoko Oya, Brian Svoboda, Hauyu Baobab Liu, Bertrand Lefloch, Serena Viti, Yichen Zhang, Cecilia Ceccarelli, Claudio Codella, Claire J. Chandler, Nami Sakai, Yuri Aikawa, Felipe O. Alves, Nadia Balucani, Eleonora Bianchi, Mathilde Bouvier, Gemma Busquet, Paola Caselli, Emmanuel Caux, Steven Charnley, Spandan Choudhury, Nicolas Cuello, Marta De Simone, Francois Dulieu, Aurora Durán, Lucy Evans, Cécile Favre, Davide Fedele, Siyi Feng, Francesco Fontani, Logan Francis, Tetsuya Hama, Tomoyuki Hanawa, Eric Herbst, Shingo Hirano, Tomoya Hirota, Andrea Isella, Izaskun Jímenez-Serra, Doug Johnstone, Claudine Kahane, Romane Le Gal, Laurent Loinard, Ana López-Sepulcre, Luke T. Maud, María José Maureira, Francois Menard, Seyma Mercimek, Anna Miotello, George Moellenbrock, Shoji Mori, Nadia M. Murillo, Riouhei Nakatani, Hideko Nomura, Yasuhiro Oba, Ross O’Donoghue, Satoshi Ohashi, Yuki Okoda, Juan Ospina-Zamudio, Jaime Pineda, Linda Podio, Albert Rimola, Takeshi Sakai, Dominique Segura-Cox, Yancy Shirley, Vianney Taquet, Leonardo Testi, Charlotte Vastel, Naoki Watanabe, Yoshimasa Watanabe, Arezu Witzel, Ci Xue, Bo Zhao, Satoshi Yamamoto
    The Astrophysical Journal 934 1 70 - 70 2022年07月01日 
    Abstract The chemical diversity of low-mass protostellar sources has so far been recognized, and environmental effects are invoked as its origin. In this context, observations of isolated protostellar sources without the influence of nearby objects are of particular importance. Here, we report the chemical and physical structures of the low-mass Class 0 protostellar source IRAS 16544−1604 in the Bok globule CB 68, based on 1.3 mm Atacama Large Millimeter/submillimeter Array observations at a spatial resolution of ∼70 au that were conducted as part of the large program FAUST. Three interstellar saturated complex organic molecules (iCOMs), CH3OH, HCOOCH3, and CH3OCH3, are detected toward the protostar. The rotation temperature and the emitting region size for CH3OH are derived to be 131 ± 11 K and ∼10 au, respectively. The detection of iCOMs in close proximity to the protostar indicates that CB 68 harbors a hot corino. The kinematic structure of the C18O, CH3OH, and OCS lines is explained by an infalling–rotating envelope model, and the protostellar mass and the radius of the centrifugal barrier are estimated to be 0.08–0.30 M and <30 au, respectively. The small radius of the centrifugal barrier seems to be related to the small emitting region of iCOMs. In addition, we detect emission lines of c-C3H2 and CCH associated with the protostar, revealing a warm carbon-chain chemistry on a 1000 au scale. We therefore find that the chemical structure of CB 68 is described by a hybrid chemistry. The molecular abundances are discussed in comparison with those in other hot corino sources and reported chemical models.
  • W. M. C. Sameera, Bethmini Senevirathne, Thanh Nguyen, Yasuhiro Oba, Atsuki Ishibashi, Masashi Tsuge, Hiroshi Hidaka, Naoki Watanabe
    Frontiers in Astronomy and Space Sciences 9 2022年05月30日 
    Heterogeneous radical processes on ice surfaces play a vital role in the formation of building blocks of the biologically relevant molecules in space. Therefore, quantitative mechanistic details of the radical binding and radical reactions on ices are crucial in rationalizing the chemical evolution in the Universe. The radical chemistry on ice surfaces was explored at low temperatures by combining quantum chemical calculations and laboratory experiments. A range of binding energies was observed for OH, HCO, CH3, and CH3O radicals binding on ices. Computed reaction paths of the radical reactions on ices, OCS + H and PH3 + D, explained the experimentally observed products. In both radical reactions, quantum tunnelling plays a key role in achieving the reactions at low temperatures. Our findings give quantitative insights into radical chemistry on ice surfaces in interstellar space and the planetary atmospheres.
  • Satoshi Ohashi, Claudio Codella, Nami Sakai, Claire J. Chandler, Cecilia Ceccarelli, Felipe Alves, Davide Fedele, Tomoyuki Hanawa, Aurora Durán, Cécile Favre, Ana López-Sepulcre, Laurent Loinard, Seyma Mercimek, Nadia M. Murillo, Linda Podio, Yichen Zhang, Yuri Aikawa, Nadia Balucani, Eleonora Bianchi, Mathilde Bouvier, Gemma Busquet, Paola Caselli, Emmanuel Caux, Steven Charnley, Spandan Choudhury, Nicolas Cuello, Marta De Simone, Francois Dulieu, Lucy Evans, Siyi Feng, Francesco Fontani, Logan Francis, Tetsuya Hama, Eric Herbst, Shingo Hirano, Tomoya Hirota, Muneaki Imai, Andrea Isella, Izaskun Jímenez-Serra, Doug Johnstone, Claudine Kahane, Romane Le Gal, Bertrand Lefloch, Luke T. Maud, Maria Jose Maureira, Francois Menard, Anna Miotello, George Moellenbrock, Shoji Mori, Riouhei Nakatani, Hideko Nomura, Yasuhiro Oba, Ross O’Donoghue, Yuki Okoda, Juan Ospina-Zamudio, Yoko Oya, Jaime Pineda, Albert Rimola, Takeshi Sakai, Dominique Segura-Cox, Yancy Shirley, Brian Svoboda, Vianney Taquet, Leonardo Testi, Charlotte Vastel, Serena Viti, Naoki Watanabe, Yoshimasa Watanabe, Arezu Witzel, Ci Xue, Bo Zhao, Satoshi Yamamoto
    The Astrophysical Journal 927 1 54 - 54 2022年03月01日 
    Abstract We report a study of the low-mass Class 0 multiple system VLA 1623AB in the Ophiuchus star-forming region, using H13CO+ (J = 3–2), CS (J = 5–4), and CCH (N = 3–2) lines as part of the ALMA Large Program FAUST. The analysis of the velocity fields revealed the rotation motion in the envelope and the velocity gradients in the outflows (about 2000 au down to 50 au). We further investigated the rotation of the circumbinary VLA 1623A disk, as well as the VLA 1623B disk. We found that the minor axis of the circumbinary disk of VLA 1623A is misaligned by about 12° with respect to the large-scale outflow and the rotation axis of the envelope. In contrast, the minor axis of the circumbinary disk is parallel to the large-scale magnetic field according to previous dust polarization observations, suggesting that the misalignment may be caused by the different directions of the envelope rotation and the magnetic field. If the velocity gradient of the outflow is caused by rotation, the outflow has a constant angular momentum and the launching radius is estimated to be 5–16 au, although it cannot be ruled out that the velocity gradient is driven by entrainments of the two high-velocity outflows. Furthermore, we detected for the first time a velocity gradient associated with rotation toward the VLA 16293B disk. The velocity gradient is opposite to the one from the large-scale envelope, outflow, and circumbinary disk. The origin of its opposite gradient is also discussed.
  • Kenji Furuya, Yasuhiro Oba, Takashi Shimonishi
    The Astrophysical Journal 926 2 171 - 171 2022年02月01日 
    Abstract Nonthermal desorption of molecules from icy grain surfaces is required to explain molecular line observations in the cold gas of star-forming regions. Chemical desorption is one of the nonthermal desorption processes and is driven by the energy released by chemical reactions. After an exothermic surface reaction, the excess energy is transferred to products’ translational energy in the direction perpendicular to the surface, leading to desorption. The desorption probability of product species, especially that of product species from water-ice surfaces, is not well understood. This uncertainty limits our understanding of the interplay between gas-phase and ice-surface chemistry. In the present work, we constrain the desorption probability of H2S and PH3 per reaction event on porous amorphous solid water (ASW) by numerically simulating previous laboratory experiments. Adopting the microscopic kinetic Monte Carlo method, we find that the desorption probabilities of H2S and PH3 from porous ASW per hydrogen-addition event of the precursor species are 3% ± 1.5% and 4% ± 2%, respectively. These probabilities are consistent with a theoretical model of chemical desorption proposed in the literature if ∼7% of energy released by the reactions is transferred to the translational excitation of the products. As a byproduct, we find that approximately 70% (40%) of adsorption sites for atomic H on porous ASW should have a binding energy lower than ∼300 K (∼200 K). The astrochemical implications of our findings are briefly discussed.
  • Akira Kouchi, Yuki Kimura, Kensei Kitajima, Hiroyasu Katsuno, Hiroshi Hidaka, Yasuhiro Oba, Masashi Tsuge, Tomoya Yamazaki, Kazuyuki Fujita, Tetsuya Hama, Yukihiro Takahashi, Shunichi Nakatsubo, Naoki Watanabe
    Frontiers in Chemistry 9 2021年12月08日 
    The occurrence of hydrogen atom-ordered form of ice Ih, ice XI, in the outer Solar System has been discussed based on laboratory experiments because its ferroelectricity influences the physical processes in the outer Solar System. However, the formation of ice XI in that region is still unknown due to a lack of formation conditions at temperatures higher than 72 K and the effect of UV-rays on the phase transition from ice I to ice XI. As a result, we observed the UV-irradiation process on ice Ih and ice Ic using a newly developed ultra-high vacuum cryogenic transmission electron microscope. We found that ice Ih transformed to ice XI at temperatures between 75 and 140 K with a relatively small UV dose. Although ice Ic partially transformed to ice XI at 83 K, the rate of transformation was slower than for ice Ih. These findings point to the formation of ice XI at temperatures greater than 72 K via UV irradiation of ice I crystals in the Solar System; icy grains and the surfaces of icy satellites in the Jovian and Saturnian regions.
  • Thanh Nguyen, Yasuhiro Oba, W. M. C. Sameera, Akira Kouchi, Naoki Watanabe
    The Astrophysical Journal 2021年12月01日 [査読有り]
  • Akira Kouchi, Masashi Tsuge, Tetsuya Hama, Yasuhiro Oba, Satoshi Okuzumi, Sin-iti Sirono, Munetake Momose, Naoki Nakatani, Kenji Furuya, Takashi Shimonishi, Tomoya Yamazaki, Hiroshi Hidaka, Yuki Kimura, Ken-ichiro Murata, Kazuyuki Fujita, Shunichi Nakatsubo, Shogo Tachibana, Naoki Watanabe
    ASTROPHYSICAL JOURNAL 918 2 2021年09月 
    It has been implicitly assumed that ices on grains in molecular clouds and protoplanetary disks are formed by homogeneous layers regardless of their composition or crystallinity. To verify this assumption, we observed the H2O deposition onto refractory substrates and the crystallization of amorphous ices (H2O, CO2, and CO) using an ultra-high-vacuum transmission electron microscope. In the H2O-deposition experiments, we found that three-dimensional islands of crystalline ice (I-c) were formed at temperatures above 130 K. The crystallization experiments showed that uniform thin films of amorphous CO and H2O became three-dimensional islands of polyhedral crystals; amorphous CO2, on the other hand, became a thin film of nano-crystalline CO2 covering the amorphous H2O. Our observations show that crystal morphologies strongly depend not only on the ice composition but also on the substrate. Using experimental data concerning the crystallinity of deposited ices and the crystallization timescale of amorphous ices, we illustrated the criteria for ice crystallinity in space and outlined the macroscopic morphology of icy grains in molecular clouds as follows: amorphous H2O covered the refractory grain uniformly, CO2 nano-crystals were embedded in the amorphous H2O, and a polyhedral CO crystal was attached to the amorphous H2O. Furthermore, a change in the grain morphology in a protoplanetary disk is shown. These results have important implications for the chemical evolution of molecules, nonthermal desorption, collision of icy grains, and sintering.
  • Thanh Nguyen, Yasuhiro Oba, W. M. C. Sameera, Akira Kouchi, Naoki Watanabe
    ASTROPHYSICAL JOURNAL 918 2 2021年09月 
    Phosphine (PH3) is an important molecule in the chemistry of phosphorus (P)-bearing species in the interstellar medium. Interstellar PH3 is thought to primarily form on icy grains, where several surface processes may occur during and after its formation. To better understand the physicochemical behavior of PH3 on icy grains in dense molecular clouds, we performed experimental and computational studies on the reactions of phosphine with H and D atoms at low temperatures. We found that phosphine and its deuterated isotopologue PD3 are released into the gas phase from icy surfaces (porous amorphous, compact amorphous, and crystalline ice) via chemical desorption. Even though the effective desorption cross section did not vary between the different icy surfaces, the desorption fraction was smallest for porous amorphous ice. We confirmed that, at 10 K on icy surfaces, H-D substitution reactions of PH3 and D-H substitution reactions of PD3 occurred following reactions with D and H atoms, respectively. Because the activation barrier for the abstraction of H or D atoms from phosphine is similar to 1500 K, quantum tunneling should play a role at low temperatures. Under the present experimental conditions, the H-D substitution reaction of PH3 was slightly slower than the D-H substitution reaction of PD3. Therefore, the rates of the H-D and D-H substitution reactions should not be constrained by tunneling reactions but rather by other elementary processes such as atom diffusion on ice. Our experimental results suggest the possible presence of a deuterated phosphine isotopologue (PH2D) in PH3-rich interstellar environments.
  • Akira Kouchi, Masashi Tsuge, Tetsuya Hama, Hiromasa Niinomi, Naoki Nakatani, Takashi Shimonishi, Yasuhiro Oba, Yuki Kimura, Sin-iti Sirono, Satoshi Okuzumi, Munetake Momose, Kenji Furuya, Naoki Watanabe
    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 505 1 1530 - 1542 2021年07月 
    The crystallinity and morphology of solid carbon monoxide (CO) on icy interstellar grains were examined by observing the deposition, crystallization, and UV and electrons irradiation of solid CO using transmission electron microscopy. Herein, we found that solid CO deposited in molecular clouds was crystalline, and that even if amorphous CO was deposited, amorphous CO crystallized within 10(3) yr at 10 K. Conversely, crystalline CO was not amorphized by UV rays or electron beam at 10 K. These results indicated the occurrence of chiral crystalline CO instead of amorphous CO in space. Furthermore, the large surface diffusion coefficients of CO on eamorphous H2O and crystalline CO at 10 K facilitated the morphological equilibration of crystalline CO. Bad wetting of crystalline CO with amorphous H2O proved that the morphology of the ice grains was not spherical with an onion-like structure, as hitherto assumed, but rather it was a polyhedral crystalline CO attached to amorphous H2O. This has important implications for phenomena associated with the collision and subsequent sticking between ice grains, surface chemical reactions, non-thermal desorption of molecules and the origin of homochirality in interstellar biomolecules.
  • Yuki Okoda, Yoko Oya, Logan Francis, Doug Johnstone, Shu-ichiro Inutsuka, Cecilia Ceccarelli, Claudio Codella, Claire Chandler, Nami Sakai, Yuri Aikawa, Felipe O. Alves, Nadia Balucani, Eleonora Bianchi, Mathilde Bouvier, Paola Caselli, Emmanuel Caux, Steven Charnley, Spandan Choudhury, Marta De Simone, Francois Dulieu, Aurora Duran, Lucy Evans, Cecile Favre, Davide Fedele, Siyi Feng, Francesco Fontani, Tetsuya Hama, Tomoyuki Hanawa, Eric Herbst, Tomoya Hirota, Muneaki Imai, Andrea Isella, Izaskun Jimenez-Serra, Claudine Kahane, Bertrand Lefloch, Laurent Loinard, Ana Lopez-Sepulcre, Luke T. Maud, Maria Jose Maureira, Francois Menard, Seyma Mercimek, Anna Miotello, George Moellenbrock, Shoji Mori, Nadia M. Murillo, Riouhei Nakatani, Hideko Nomura, Yasuhiro Oba, Ross O'Donoghue, Satoshi Ohashi, Juan Ospina-Zamudio, Jaime E. Pineda, Linda Podio, Albert Rimola, Takeshi Sakai, Dominique Segura-Cox, Yancy Shirley, Brian Svoboda, Vianney Taquet, Leonardo Testi, Charlotte Vastel, Serena Viti, Naoki Watanabe, Yoshimasa Watanabe, Arezu Witzel, Ci Xue, Yichen Zhang, Bo Zhao, Satoshi Yamamoto
    ASTROPHYSICAL JOURNAL 910 1 2021年03月 
    We have observed the very low-mass Class 0 protostar IRAS 15398-3359 at scales ranging from 50 to 1800 au, as part of the Atacama Large Millimeter/Submillimeter Array Large Program FAUST. We uncover a linear feature, visible in H2CO, SO, and (CO)-O-18 line emission, which extends from the source in a direction almost perpendicular to the known active outflow. Molecular line emission from H2CO, SO, SiO, and CH3OH further reveals an arc-like structure connected to the outer end of the linear feature and separated from the protostar, IRAS 15398-3359, by 1200 au. The arc-like structure is blueshifted with respect to the systemic velocity. A velocity gradient of 1.2 km s(-1) over 1200 au along the linear feature seen in the H2CO emission connects the protostar and the arc-like structure kinematically. SO, SiO, and CH3OH are known to trace shocks, and we interpret the arc-like structure as a relic shock region produced by an outflow previously launched by IRAS 15398-3359. The velocity gradient along the linear structure can be explained as relic outflow motion. The origins of the newly observed arc-like structure and extended linear feature are discussed in relation to turbulent motions within the protostellar core and episodic accretion events during the earliest stage of protostellar evolution.
  • Yoshinori Takano, Yasuhiro Oba, Satoshi Furota, Hiroshi Naraoka, Nanako Ogawa, Thomas M. Blattmann, Naohiko Ohkouchi
    International Journal of Mass Spectrometry 116529 - 116529 2021年01月 [査読有り]
  • Yasuhiro Oba, Yoshinori Takano, Hiroshi Naraoka, Yoshihiro Furukawa, Daniel P. Glavin, Jason P. Dworkin, Shogo Tachibana
    Nature Communications 11 1 2020年12月 [査読有り]
     
    AbstractDespite extensive studies on the formation of organic molecules in various extraterrestrial environments, it still remains under debate when, where, and how such molecules were abiotically formed. A key molecule to solve the problem, hexamethylenetetramine (HMT) has not been confirmed in extraterrestrial materials despite extensive laboratory experimental evidence that it can be produced in interstellar or cometary environments. Here we report the first detection of HMT and functionalized HMT species in the carbonaceous chondrites Murchison, Murray, and Tagish Lake. While the part-per-billion level concentration of HMT in Murchison and Tagish Lake is comparable to other related soluble organic molecules like amino acids, these compounds may have eluded detection in previous studies due to the loss of HMT during the extraction processes. HMT, which can yield important molecules for prebiotic chemistry such as formaldehyde and ammonia upon degradation, is a likely precursor of meteoritic organic compounds of astrochemical and astrophysical interest.
  • Masashi Tsuge, Thanh Nguyen, Yasuhiro Oba, Tetsuya Hama, Akira Kouchi, Naoki Watanabe
    Chemical Physics Letters 760 137999 - 137999 2020年12月 [査読有り]
  • Hideyuki Nakano, Naoki Hirakawa, Yasuhiro Matsubara, Shigeru Yamashita, Takuo Okuchi, Kenta Asahina, Ryo Tanaka, Noriyuki Suzuki, Hiroshi Naraoka, Yoshinori Takano, Shogo Tachibana, Tetsyua Hama, Yasuhiro Oba, Yuki Kimura, Naoki Watanabe, Akira Kouchi
    Scientific Reports 10 7755  2020年12月 [査読有り][通常論文]
  • Thanh Nguyen, Yasuhiro Oba, Takashi Shimonishi, Akira Kouchi, Naoki Watanabe
    ASTROPHYSICAL JOURNAL LETTERS 898 2 2020年08月 [査読有り][通常論文]
     
    Phosphine (PH3), an important molecule for the chemistry of phosphorus (P)-bearing species in the interstellar medium (ISM) is considered to form primarily on interstellar grains. However, no report exists on the processes of PH(3)formation on grains. Here, we experimentally studied the reactions of hydrogen (H) atoms and PH(3)molecules on compact amorphous solid water, with a particular focus on the chemical desorption of PH(3)at 10-30 K. After exposure to H atoms for 120 minutes, up to 50% of solid PH(3)was lost from the icy surface. On the basis of experiments using deuterium atoms, it was concluded that the loss of PH(3)resulted from chemical desorption through the reactions PH3+ H -> PH2 + H(2)and/or PH2+ H -> PH3. The effective desorption cross-section was similar to 5 x 10(-17)cm(2), which is three times larger than that of hydrogen sulfide measured under similar experimental conditions. The present results suggest that the formation of PH3, and possibly PH(2)and PH, followed by their desorption from icy grains, may contribute to the formation of PN and PO in the gas phase, and thus may play a role in the P chemistry of the ISM.
  • Nucleobase synthesis in interstellar ices
    Y. Oba, Y. Takano, H. Naraoka, N. Watanabe, A. Kouchi
    Nature Communications 10 4413  2019年09月 [査読有り][通常論文]
  • Physico-chemical behavior of hydrogen sulfide induced by reactions with H and D atoms on different types of ice surfaces at low temperature
    Y. Oba, T. Tomaru, A. Kouchi, N. Watanabe
    Astrophysical Journal 874 8pp  2019年04月 [査読有り][通常論文]
  • なぜ宇宙空間の分子はガス状で存在できるのか?星間塵上の化学反応によるガスの放出を放出を実証
    渡部直樹, 大場康弘
    化学 73 2018年06月 [査読有り][通常論文]
  • Y. Oba, T. Tomaru, T. Lamberts, A. Kouchi, N. Watanabe
    Nature Astronomy 2 3 228 - 232 2018年03月01日 [査読有り][通常論文]
     
    In molecular clouds at temperatures as low as 10 K, all species except hydrogen and helium should be locked in the heterogeneous ice on dust grain surfaces. Nevertheless, astronomical observations have detected over 150 different species in the gas phase in these clouds. The mechanism by which molecules are released from the dust surface below thermal desorption temperatures to be detectable in the gas phase is crucial for understanding the chemical evolution in such cold clouds. Chemical desorption, caused by the excess energy of an exothermic reaction, was first proposed as a key molecular release mechanism almost 50 years ago 1 . Chemical desorption can, in principle, take place at any temperature, even below the thermal desorption temperature. Therefore, astrochemical network models commonly include this process 2,3 . Although there have been a few previous experimental efforts 4-6, no infrared measurement of the surface (which has a strong advantage to quantify chemical desorption) has been performed. Here, we report the first infrared in situ measurement of chemical desorption during the reactions H + H2S → HS + H2 (reaction 1) and HS + H → H2S (reaction 2), which are key to interstellar sulphur chemistry 2,3 . The present study clearly demonstrates that chemical desorption is a more efficient process for releasing H2S into the gas phase than was previously believed. The obtained effective cross-section for chemical desorption indicates that the chemical desorption rate exceeds the photodesorption rate in typical interstellar environments.
  • Yasuhiro Oba, Yoshinori Takano, Hiroshi Naraoka, Akira Kouchi, Naoki Watanabe
    ASTROPHYSICAL JOURNAL 849 2 9pp  2017年11月 [査読有り][通常論文]
     
    Hexamethylenetetramine (HMT) is a representative product after the photolysis of interstellar ice analogs containing methanol followed by warming-up to room temperature. Since interstellar methanol is often significantly enriched in deuterium (D), the HMT photoproduct is expected to inherit D atoms from deuterated methanol. However, D fractionation upon the formation of HMT is not well understood, especially when it is produced from partly deuterated methanol isotopologues such as CH2DOH and CH3OD. Here, we experimentally studied the composition of deuterated HMT (d(n)-HMT, where n is the number of D atoms) at the isotopologue level formed by the photolysis of ice mixtures containing deuterated methanol, CH2DOH or CH3OD, at 10 or 77 K. The analyses were performed using a state-of-the-art high-resolution mass spectrometer coupled with a compoundspecific separation technique. The formation of dn-HMT (n = 0-8) was confirmed under all experimental conditions. In addition, methyl-and hydroxyl-substituted HMT and their deuterated isotopologues were also obtained in the products. The deuterium enrichment was outstanding when CH2DOH was used rather than CH3OD, and when photolysis was performed at 77 K rather than 10 K. We found that the deuteration level of the formed HMT far exceeded that of the reactants under the present experimental conditions. These results obtained during stable isotope probing of deuterium strongly suggest that HMT can play a role as an organic pool of interstellar D atoms. These may be distributed into other chemical species through molecular evolution in space.
  • Shogo Tachibana, Akira Kouchi, Tetsuya Hama, Yasuhiro Oba, Laurette Piani, Iyo Sugawara, Yukiko Endo, Hiroshi Hidaka, Yuki Kimura, Ken-Ichiro Murata, Hisayoshi Yurimoto, Naoki Watanabe
    Science advances 3 9 eaao2538  2017年09月 [査読有り][通常論文]
     
    Interstellar ice is believed to be a cradle of complex organic compounds, commonly found within icy comets and interstellar clouds, in association with ultraviolet (UV) irradiation and subsequent warming. We found that UV-irradiated amorphous ices composed of H2O, CH3OH, and NH3 and of pure H2O behave like liquids over the temperature ranges of 65 to 150 kelvin and 50 to 140 kelvin, respectively. This low-viscosity liquid-like ice may enhance the formation of organic compounds including prebiotic molecules and the accretion of icy dust to form icy planetesimals under certain interstellar conditions.
  • 大場 康弘, 高野 淑識, 奈良岡 浩, 渡部 直樹, 香内 晃
    日本地球化学会年会要旨集 64 131 - 131 一般社団法人日本地球化学会 2017年 

    重水素一置換メタノールCH2DOHを含む疑似星間塵氷の光化学反応で生成するヘキサメチレンテトラミン(HMT:C6H12N4)の重水素存在度を報告する。10Kの反応基板上に混合ガス(H2O:CO:NH3:CH2DOH=5:2:2:2)を蒸着し,疑似星間塵氷を作製した。それと同時に真空紫外光を照射し,星間塵上での光化学反応を再現した。生成したHMTには非常に多くの重水素が含まれていたことから,本研究はHMTが化学進化における優れた重水素キャリアとなることを強く示唆した。

  • Yasuhiro Oba, Naoki Watanabe, Akira Kouchi
    CHEMICAL PHYSICS LETTERS 662 14 - 18 2016年10月 [査読有り][通常論文]
     
    We report an experimental study on the catalytic effect of solid water on the reactivity of hydrogen abstraction (H-abstraction) from dimethyl ether (DME) in the low-temperature solid DME-H2O complex. When DME reacted with deuterium atoms on a surface at 15-25 K, it was efficiently deuterated via successive tunneling H-abstraction and deuterium (D)-addition reactions. The 'effective rate constant for DME-H2O + D was found to be about 20 times smaller than that of pure DME + D. This provides the first evidence that the presence of solid water has a negative catalytic effect on tunneling H-abstraction reactions. (C) 2016 Elsevier B.V. All rights reserved.
  • Yasuhiro Oba, Kazuya Osaka, Takeshi Chigai, Akira Kouchi, Naoki Watanabe
    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 462 1 689 - 695 2016年10月 [査読有り][通常論文]
     
    Ethanol (CH3CH2OH) is one of the most abundant complex organic molecules in star-forming regions. Despite its detection in the gas phase only, ethanol is believed to be formed by low temperature grain-surface reactions. Methanol, the simplest alcohol, has been a target for observational, experimental, and theoretical studies in view of its deuterium enrichment in the interstellar medium; however, the deuterium chemistry of ethanol has not yet been an area of focus. Recently, deuterated dimethyl ether, a structural isomer of ethanol, was found in star forming regions, indicating that deuterated ethanol can also be present in those environments. In this study, we performed laboratory experiments on the deuterium fractionation of solid ethanol at low temperatures through a reaction with deuterium (D) atoms at 10 K. Hydrogen (II)-D substitution, which increases the deuteration level, was found to occur on the ethyl group but not on the hydroxyl group. In addition, when deuterated ethanol (e.g. CD3CD2OD) solid was exposed to H atoms at 10 K, D-H substitution that reduced the deuteration level occurred on the ethyl group. Based on the results, it is likely that deuterated ethanol is present even under H-atom-dominant conditions in the interstellar medium.
  • Yasuhiro Oba, Yoshinori Takano, Naoki Watanabe, Akira Kouchi
    ASTROPHYSICAL JOURNAL LETTERS 827 1 L18(7pp)  2016年08月 [査読有り][通常論文]
     
    Deuterium (D) atoms in interstellar deuterated methanol might be distributed into complex organic molecules through molecular evolution by photochemical reactions in interstellar grains. In this study, we use a state-of-the-art high-resolution mass spectrometer coupled with a high-performance liquid chromatography system to quantitatively analyze amino acids and their deuterated isotopologues formed by the photolysis of interstellar ice analogs containing singly deuterated methanol CH2DOH at 10 K. Five amino acids (glycine, alpha-alanine, beta-alanine, sarcosine, and serine) and their deuterated isotopologues whose D atoms are bound to carbon atoms are detected in organic residues formed by photolysis followed by warming up to room temperature. The abundances of singly deuterated amino acids are in the range of 0.3-1.1 relative to each nondeuterated counterpart, and the relative abundances of doubly and triply deuterated species decrease with an increasing number of D atoms in a molecule. The abundances of amino acids increase by a factor of more than five upon the hydrolysis of the organic residues, leading to decreases in the relative abundances of deuterated species for alpha-alanine and beta-alanine. On the other hand, the relative abundances of the deuterated isotopologues of the other three amino acids did not decrease upon hydrolysis, indicating different formation mechanisms of these two groups upon hydrolysis. The present study facilitates both qualitative and quantitative evaluations of D fractionation during molecular evolution in the interstellar medium.
  • Y. Oba, N. Watanabe, Y. Osamura, A.Kouchi
    Chem. Phys. Lett. 634 53 - 59 2015年08月 [査読有り][通常論文]
     
    We report experimental evidence that chiral glycine (NH2CHDCOOH) is formed by the surface reaction of normal glycine (NH2CH2COOH) solid with deuterium (D) atom at 12K under the simulative conditions of interstellar molecular clouds. Chiral glycine formation is most likely initiated by the tunneling abstraction reaction of H atom by D atom followed by the addition of D atom to the glycine radical (NH2CHCOOH). Given that chiral glycine can form in such a primordial low-temperature environment, it might source molecular chirality as molecular clouds evolve into planetary systems. (C) 2015 Elsevier B.V. All rights reserved.
  • Yasuhiro Oba, Kazuya Osaka, Naoki Watanabe, Takeshi Chigai, Akira Kouchi
    FARADAY DISCUSSIONS 168 185 - 204 2014年08月 [査読有り][通常論文]
     
    We performed laboratory experiments on the formation of water and its isotopologues by surface reactions of hydrogen peroxide (H2O2) with hydrogen (H) atoms and their deuterated counterparts (D2O2, D) at 10-30 K. High-purity H2O2 (>95%) was prepared in situ by the codeposition of molecular oxygen and H atoms at relatively high temperatures (45-50 K). We determined that the high-purity H2O2 solid reacts with both H and deuterium (D) atoms at 10-30 K despite the large activation barriers (similar to 2000 K). Moreover, the reaction rate for H atoms is approximately 45 times faster than that for D atoms at 15 K. Thus, the observed large isotope effect indicates that these reactions occurred through quantum tunneling. We propose that the observed HDO/H2O ratio in molecular clouds might be a good tool for the estimation of the atomic D/H ratio in those environments.
  • Yasuhiro Oba, Takeshi Chigai, Yoshihiro Osamura, Naoki Watanabe, Akira Kouchi
    METEORITICS & PLANETARY SCIENCE 49 1 117 - 132 2014年01月 [査読有り][通常論文]
     
    We experimentally studied hydrogen (H)-deuterium (D) substitution reactions of solid methylamine (CH3NH2) under astrophysically relevant conditions. We also calculated the potential energy surface for the H-D substitution reactions of methylamine isotopologues using quantum chemical methods. Despite the relatively large energy barrier of more than 18kJmol(-1), CH3NH2 reacted with D atoms to yield deuterated methylamines at 10K, suggesting that the H-D substitution reaction proceeds through quantum tunneling. Deuterated methylamines reacted with H atoms as well. On the basis of present results, we propose that methylamine has potential for D enrichment through atomic surface reactions on interstellar grains at very low temperatures in molecular clouds. D enrichment would occur in particular in the methyl group of methylamine.
  • 大場 康弘, 渡部 直樹, 香内 晃
    日本地球化学会年会要旨集 61 168 - 168 日本地球化学会 2014年 
    本講演では,星間塵表面反応で生成する水分子の水素同位体組成について,これまでの実験結果をもとに詳細な議論をおこなう。一般的に星間分子は分子生成時および分子生成後に重水素濃集可能であるが,水分子に関しては,極低温の星間塵表面では分子生成時に限定される。水分子は3つの経路でおもに生成するが,うち2つの生成反応は極低温では熱的におこりえず,量子力学的なトンネル効果が不可欠である。量子力学的トンネル反応には大きな同位体効果が期待されるため,生成する水分子の水素同位体組成を議論する際には注意が必要である。
  • Y.Oba, N.Watanabe, T.Hama, K.Kuwahata, H.Hidaka, A.Kouchi
    The Astrophysical Journal 749 1 67 - (12pp) 2012年 [査読有り][通常論文]
  • 渡部直樹, 香内晃, 羽馬哲也, 日高宏, 大場康弘, 千貝健
    表面科学 33 12 662 - 668 2012年 [査読無し][通常論文]
  • 大場 康弘, 渡部 直樹, 香内 晃, 羽馬 哲也, ピロネロ バレリオ
    地球化学 45 4 213 - 226 日本地球化学会 2011年12月 [査読有り][通常論文]
     
    Since the first detection in interstellar medium in 1989, solid CO2 has been found in various lines of sight and regarded as one of the main constituent in icy grain mantles in interstellar clouds. Due to the low efficiency in the formation of CO2 in the gas phase and relatively high abundance of CO in icy grain mantles, it is generally accepted that CO2 forms on the surface of icy grain mantles in interstellar clouds. CO2 formation on/in icy grain mantles has been extensively studied experimentally, with the aid of energetic sources such as UV or cosmic-rays, and also without them. In this review, we summarize experimental results on the formation of CO2 on cold surfaces through energetic and non-energetic processes under the simulative conditions of interstellar molecular clouds.
  • 大場 康弘
    Researches in Organic Geochemistry 27 103 - 115 2011年09月 [査読有り][通常論文]
  • Formation of H2O ice through the surface reaction O2 + H at low temperatures: Reaction kinetics and structure of the ice
    Y. Oba, N. Miyauchi, T. Chigai, H. Hidaka, N. Watanabe, A. Kouchi
    Physics and Chemistry of ice 2010 369 - 378 2011年 [査読有り][通常論文]
  • 大場 康弘, 渡部 直樹, 香内 晃
    日本地球化学会年会要旨集 58 291 - 291 日本地球化学会 2011年 
    H2Oは星間塵アイスマントルの主要な構成成分である。H2Oはその存在量を気相反応のみでは説明できないことから,星間塵表面での反応で生成したと考えられている。本研究では,高密度星間分子雲で主要な経路だと考えられている,ヒドロキシルラジカル(OH)と水素分子(H2)の反応による,H2O生成に関する実験結果を紹介する。実験は,超高真空・極低温環境のアルミニウム基板表面でおこなった。
  • Y.Oba, N.Watanabe, A.Kouchi, T.Hama, V.Pirronello
    The Astrophysical Journal 722 2,Pt.1 1598 - 1606 2010年10月 [査読有り][通常論文]
  • Oba Y, Watanabe N, Kouchi A, Hama T, Pirronello V
    The Astrophysical Journal 712 2,Pt.2 L174 - L178 2010年04月 [査読有り][通常論文]
  • Eui-Seong Moon, Heon Kang, Yasuhiro Oba, Naoki Watanabe, Akira Kouchi
    ASTROPHYSICAL JOURNAL 713 2 906 - 911 2010年04月 [査読有り][通常論文]
     
    We present direct evidence for ammonium ion (NH4+) formation through ultraviolet (UV) photolysis of NH3-H2O mixture ice that does not contain acids. NH4+ forms by the reaction of NH3 with protonic defects (H3O+) in the UV-photolyzed ice. Our observations may explain the deficient counter-anions in interstellar ice relative to the abundance of NH4+. Also, H3O+ may play an important role in the acid-base chemistry of interstellar ice in UV-irradiating environments. IR absorption results suggest that NH4+ is a potential contributor to the interstellar 6.85 mu m band but is not a dominant component.
  • Stephen R. Parker, Christopher H. Gammons, Simon R. Poulson, Michael D. DeGrandpre, Charmaine L. Weyer, M. Garrett Smith, John N. Babcock, Yasuhiro Oba
    CHEMICAL GEOLOGY 269 1-2 22 - 32 2010年01月 [査読有り][通常論文]
     
    Rates of diel (24-h) biogeochemical processes in rivers and their effect on daily changes in the concentration of metals and metalloids have been well documented in the literature over the last 20 years. Investigations into the effects of these processes on aquatic systems and the underlying mechanisms that control the processes can significantly improve our understanding of how natural aquatic environments function and will respond to changing environmental conditions and anthropogenic impacts. Daily changes in the rates of biogeochemical processes have, more recently, been shown to influence the stable isotope composition of dissolved oxygen and dissolved inorganic carbon in natural waters. Here we present a comprehensive picture of the persistence and reproducibility of diel cycles of the (18)O composition of dissolved molecular oxygen (delta(18)O-DO) and the (13)C composition of dissolved inorganic carbon (delta(13)C-DIC) across five Montana, USA rivers investigated over a 4-year period. A mesocosm experiment showed the same behavior in delta(13)O-DO and delta(13)C-DIC as seen in riverine settings across light and dark periods. A cross plot of delta(18)O-DO and delta(13)C-DIC from each stream exhibits a clockwise elliptical pattern which is attributed to the daily changes in the balance of metabolic rates as well as air-water gas exchange. The amplitude of the change in the isotope composition is shown to be directly related to the trophic state of the river and a relationship between net productivity and diel changes in delta(18)O-DO and delta(13)C-DIC is presented. This relationship between trophic status with delta(18)O-DO, delta(13)C-DIC and production emphasizes the significance of how rates of biogeochemical processes in natural systems can influence the daily changes in the composition of surface waters. (c) 2009 Elsevier B.V. All rights reserved.
  • Kaneko, M, Oba Y, Naraoka, H
    Res.Org.Geochem. 26 73 - 79 2010年 [査読有り][通常論文]
  • Oba Y, Poulson S.R
    ChemicalGeology 268 3-4 226 - 232 2009年11月 [査読有り][通常論文]
  • Oba Y, Miyauchi N, Chigai T, Hidaka H, Watanabe N, Kouchi A
    The Astrophysical Journal 701 1 464 - 470 2009年07月 [査読有り][通常論文]
  • N. Watanabe, A. Kouchi, H. Hidaka, Oba Y, N. Miyauchi
    Journal of Physics: Conference Series 194 1 012044  2009年 [査読有り][通常論文]
  • Formation of amorphous H2O ice from the reactions of cold H atoms with solid O2 at 10K
    A. Kouchi, N. Watanabe, H. Hidaka, N. Miyauchi, Oba Y, T. Chigai
    Cosmic Dust-Near & Far, ASP Conference Series 414 338  2009年 [査読有り][通常論文]
  • 大場 康弘, 宮内 直弥, 千貝 健, 日高 宏, 渡部 直樹, 香内 晃
    地球化学 43 4 117 - 131 日本地球化学会 2009年 [査読有り][通常論文]
     
    Formation of water by reaction of oxygen molecules (O2) with hydrogen atoms (H) were investigated at low temperatures (10-40 K) in order to reveal the possible reaction pathways to yield water on grain surfaces in molecular clouds. Two types of experiments for surface reaction between O2 and H were performed: one of which was that solid O2 was deposited onto the surface, followed by H irradiations to the O2, another of which was that gaseous O2 was continuously codeposited with H onto the surface and was reacted with each other. H2O (D2O) and H2O2 (D2O2) were quickly produced through successive reactions of O2 with H (D). Reaction kinetics and isotope effect are discussed for the former experiment. For the latter experiment, the dependence of compositions of the products on the temperature and O2/H ratio, and also the structure of the H2O ice produced are examined.
  • N.Watanabe, A.Kouchi, H.Hidaka, Y.Oba, N.Miyauchi
    XXVI International Conference on Photonic, Electronic and Atomic Collisions, Journal of Physics: Conference Series 194 12044  2009年 [査読有り][通常論文]
  • Y.Oba, S.R.Poulson
    Geochimica et Cosmochimica Acta 73 1 13 - 24 2009年 [査読有り][通常論文]
  • Y.Oba, H.Naraoka
    Meteoritics and Planetary Science 44 7 943 - 953 2009年 [査読有り][通常論文]
  • 大場 康弘, 渡部 直樹, 日高 宏, 香内 晃, ピロネロ バレリオ
    日本地球化学会年会要旨集 56 66 - 66 日本地球化学会 2009年 
    二酸化炭素は分子雲中星間塵アイスマントルの主要な構成成分であるが、気相反応によってその存在量を説明することができないため、その生成には塵表面での反応が重要だと考えられている。これまでの研究では、UVなどの外部エネルギーをH2OやCOなどを含む混合氷に照射してCO2生成が確認されてきたが、外部エネルギー無しにCO2が生成するかどうかは明らかにされていなかった。本講演では、100Kに冷却されたOHラジカルとCOの固体表面上での反応でCO2生成が確認されたので、その結果について報告する。
  • A. Kouchi, Y. Oba, N. Miyauchi, H. Hidaka, N. Watanabe
    Cryobiology 59 3 370  Elsevier {BV} 2009年 [査読有り][通常論文]
  • Oba Y, Naraoka H
    Organicgeochemistry 39 5 501 - 509 2008年 [査読有り][通常論文]
  • 力石 嘉人, 大場 康弘
    Researches in Organic Geochemistry 23/24 99 - 122 日本有機地球化学会 2008年 [査読有り][通常論文]
     
    One of the most powerful techniques in the molecular isotope studies is compound-specific isotope analysis (CSIA) by gas chromatograph/isotope ratio mass spectrometer (GC/IRMS), which allows a rapid and precise determination of stable carbon, nitrogen, and hydrogen (and oxygen) isotopic compositions of individual compounds even in complex mixture of components. After commercial production of GC/IRMS in the 1990s, CSIA has explosively been used for many fields of studies, particularly among the organic geochemical community as a powerful tool for tracing sources and delivery of organic compounds in geological and geographical samples and for reconstructing paleoenvironments. However, it is also true that fundamental analytical parameters of GC/IRMS has not been known extensively, which often leads to unreliable determination of the isotopic compositions. Unfortunately, based on such unreliable determination, several studies have unconsciously reported essentially inaccurate data and associated discussion. Therefore, in this paper, we review a brief outline of GC/IRMS and associated methodologies, and summarize the instrumental factors influencing accuracy and precision of the isotope measurements. We hope that this paper is useful for applying CSIA to future studies.
  • 大場 康弘, 宮内 直弥, 千貝 健, 日高 宏, 渡部 直樹, 香内 晃
    日本地球化学会年会要旨集 55 371 - 371 日本地球化学会 2008年 
    水分子は星間塵アイスマントル中で最も多く存在する分子であるが、その生成メカニズムはいまだはっきりしない。本研究では星間塵上表面原子反応による水分子生成反応の検証を行った。酸素分子を10Kに冷却された基板上に蒸着させ、そこに水素分子をプラズマ解離させて生成する水素原子を照射した。水素原子照射により酸素分子へ水素原子が付加され、過酸化水素、水の生成が確認された。これは酸素分子への水素原子逐次付加反応O2+H->HO2、HO2+H->H2O2、H2O2+H->H2O+OHが起こったことによる。
  • Yasuhiro Oba, Hiroshi Naraoka
    GEOCHEMICAL JOURNAL 41 2 103 - 110 2007年 [査読有り][通常論文]
     
    Low molecular-weight carboxylic acids, such as acetic and propionic acids, are abundant organic compounds in carbonaceous chondrites, and are generally enriched in heavy stable isotopes (i.e., C-13 and D) relative to terrestrial organic compounds. In this study, we have determined carbon and hydrogen isotopic fractionation of acetic acid, and site-specific carbon isotopic fractionation of acetic acid, during degradation by ultraviolet (UV) light. Acetic acid became enriched in C-13 and D with increased UV exposure times. The isotopic fractionation factors (alpha) of total, methyl and carboxyl carbon of acetic acid were 0.9922, 1.0022 and 0.9823 respectively, and the alpha value for hydrogen was 0.9875. These results suggest that UV degradation could be a process for yielding C-13- and D-enrichnient of acetic acid in natural environments.
  • Y.Oba, H.Naraoka
    Meteoritics and Planetary Science 41 8 1175 - 1181 2006年08月 [査読有り][通常論文]
  • Oba Y, Naraoka H
    Rapid Communications in Mass Spectrometry 20 24 3649 - 3653 2006年 [査読有り][通常論文]
  • Y.Oba, H.Naraoka
    Researches in Organic Geochemistry 18 29 - 35 日本有機地球化学会 2003年 [査読有り][通常論文]
     
    Compound-specific hydrogen isotope analysis of polycyclic aromatic hydrocarbons (PAHs) has been established at sub-nano molar level, using gas chromatography/pyrolysis/isotope ratio mass spectrometry (GC/pyrolysis/IRMS). The analytical precision of δD value is generally less than a few ‰ at >2nmol (i.e. 20ng H) injection of pyrene and fluoranthene calibrated with co-injected 30ng H of phenanthrene and chrysene.
    Hydrogen isotope exchange of pyrene and fluoranthene with water under neutral and acidic conditions was examined with relevance to hydrogen isotopic distribution of individual PAHs in carbonaceous chondrites. Hydrogen isotope exchange between PAH and water hardly occurred at 170℃ under neutral pH condition for 2 days. However, under acidic condition (pH=2), the isotope exchange reaction occurred, where hydrogens have exchanged more easily between pyrene and water relative to between fluoranthene and water. The kinetically different behavior between pyrene and fluoranthene coincides with the two-series PAH formation mechanisms in carbonaceous chondrites inferred from carbon isotopic compositions of PAH.

講演・口頭発表等

  • Recent advances in analytical techniques for the identification of specific COMs in photochemically-processed interstellar ice analogs  [招待講演]
    Yasuhiro Oba
    43rd COSPAR Scientific Assembly 2021年01月 口頭発表(招待・特別)
  • H2S, why you no solid at 10 K? -Nonthermal desorption from interstellar icy grains  [招待講演]
    大場康弘
    JPGU 2018 Meeting 2018年05月 口頭発表(招待・特別)
  • Experimental studies on the surface reaction of hydrogen sulfide with deuterium atoms on amorphous solid water at 10 K  [招待講演]
    大場康弘
    ACS Spring National Meeting 2018年03月 口頭発表(招待・特別)
  • Formation of chiral glycine by surface reactions of normal glycine with deuterium atoms at 10 K  [招待講演]
    大場康弘
    Astrophysical Ices in the Lab (AILab) 2016年03月 口頭発表(招待・特別)
  • Formation of H2O ice on cold interstellar grains: Reaction kinetics and the structure of ice  [招待講演]
    大場康弘
    Center for Astrochemical Studies Seminar 2015年10月 口頭発表(招待・特別)
  • Co-evolution of water and organics via surface reactions on interstellar grains  [招待講演]
    大場康弘
    JPGU 2013 Meeting 2013年05月 口頭発表(招待・特別)
  • Formation of H2O ice on cold interstellar grains: reaction kinetics and the structure of ice  [招待講演]
    Y. Oba
    Workshop on Ice and Water Films 2013年05月 口頭発表(招待・特別) Seoul National Univ.
  • Laboratory study of solid H2O formation trhough quantum tunneling reaction OH + H2 at 10 K  [通常講演]
    Y. Oba, N. Watanabe, T. Hama, K. Kuwahata, H. Hidaka, A. Kouchi
    Dynamical Phenomena at Surfaces: The Role of Complexity 2012年11月 Leiden, Netherland
  • Water formation by OH + H2 on grain surfaces at 10 K: large isotope effects by quantum tunneling  [通常講演]
    Y. Oba, N. Watanabe, T. Hama, K. Kuwahata, H. Hidaka, A. Kouchi
    Workshop on Interstellar Matter 2012 2012年10月
  • Deuterium fractionation of methylamine through atomic grain-surface reactions at low temperatures: implication for the possible D/H ratio in molecular clouds  [通常講演]
    Y. Oba, T. Chigai, N. Watanabe, A. Kouchi
    Workshop on Interstellar Matter 2012 2012年10月 Sapporo, Hokkaido, Japan
  • Formation of solid H2O through surface reactions of H2 with OH radicals produced by microwave-induced H2O plasma  [通常講演]
    Y. Oba, N. Watanabe, T. Hama, K. Kuwahata, H. Hidaka, A. Kouchi
    Gordon Research Conference, Radiation Chemisty 2012年07月 Andover, NH, USA
  • Surface chemical reactions to the formation of solid H2O and its isotopologues on interstellar grains at 10 K  [通常講演]
    Y. Oba, N. Watanabe, T. Hama, K. Kuwahata, H. Hidaka, A. Kouchi
    Asteroids, Comets, Meteors (ACM) 2012 2012年05月 Niigata, JAPAN
  • Hydrogen isotope substitution of solid methylamine (CH3NH2) on a low-temperature surface  [通常講演]
    Y. Oba, N. Watanabe, T. Hama, K. Kuwahata, H. Hidaka, A. Kouchi
    Asteroids, Comets, Meteors (ACM) 2012 2012年05月 Niigata, JAPAN
  • Low-temperature surface reactions of non-energetic OH radicals of astrophysical interest  [通常講演]
    Y. Oba, N. Watanabe, T. Hama, A. Kouchi, V. Pirronello
    SASP 2012 2012年01月 Alpe d'Huez, France
  • Isotope effect on the formation of H2O isotopologues by quantum tunneling reactions of H2/HD/D2 with non-energetic OH/OD radicals at low temperatures  [通常講演]
    Y. Oba, N. Watanabe, A. Kouchi
    MATRIX 2011 2011年07月 UBC, Vancouver, Canada
  • Sequential hydrogenation of molecular oxygen on cold surfaces: reaction kinetics and structure of formed H2O ice  [通常講演]
    Y. Oba, N. Miyauchi, H. Hidaka, T. Chigai, N. Watanabe, A. Kouchi
    IAU symposium 280, The Molecular Universe 2011年05月 Toledo, Spain
  • Neutral radical-molecule reactions CO + OH on cold interstellar ices  [通常講演]
    Y. Oba, N. Watanabe, A. Kouchi, T. Hama, V. Pirronello
    IAU symposium 280, The Molecular Universe 2011年05月 Toledo, Spain
  • Experimental studies on surface reactions of CO molecules with cold OH radicals at 10-40 K  [通常講演]
    Y. Oba, N. Watanabe, A. Kouchi, T. Hama, V. Pirronello
    Pacifichem 2010 2010年12月 Honolulu, Hawaii, USA
  • Structure of H2O ice formed by surface reactions of oxygen molecules with hydrogen atoms at low temperatures  [招待講演]
    Y. Oba, N. Miyauchi, H. Hidaka, T. Chigai, N. Watanabe, A. Kouchi
    12th International Conference on the Physics and Chemistry of Ice 2010年09月 Sapporo, Hokkaido,Japan
  • Structure of H2O ice formed by surface reactions of oxygen molecules with hydrogen atoms at low temperatures  [招待講演]
    Y. Oba, N. Miyauchi, H. Hidaka, T. Chigai, N. Watanabe, A. Kouchi
    12th International Conference on the Physics and Chemistry of Ice 2010年09月 Sapporo, Hokkaido,Japan
  • Formation of CO2 and H2CO3 through non-energetic surface reactions at low temperatures  [通常講演]
    Y. Oba, N. Watanabe, A. Kouchi, T. Hama, V. Pirronello
    Workshop on Interstellar Matter 2010 2010年09月 Sapporo, Hokkaido,Japan
  • Formation of compact amorphous water ice by surface atomic reactions at low temperatures  [招待講演]
    A. Kouchi, Y. Oba, N. Miyahchi, H. Hidaka, T. Chigai, N. Watanabe
    2010 Western Pacific Geophysics Meeting 2010年06月 Taipei, Taiwan
  • Formation of compact amorphous water ice by surface atomic reactions at low temperatures  [招待講演]
    A. Kouchi, Y. Oba, N. Miyahchi, H. Hidaka, T. Chigai, N. Watanabe
    2010 Western Pacific Geophysics Meeting 2010年06月 Taipei, Taiwan
  • Surface reactions of CO molecules with OH radicals at low temperatures  [通常講演]
    Y. Oba, N. Watanabe, A. Kouchi, T. Hama, V. Pirronello
    2010 Western Pacific Geophysics Meeting 2010年06月 Taipei, Taiwan
  • Surface reactions of hydrogen atoms with oxygen molecules at low temperatures: A potential route for the H2O formation in space  [通常講演]
    Y. Oba, N. Miyauchi, H. Hidaka, T. Chigai, N. Watanabe, A. Kouchi
    Horiba-ISSP International Symposium on "Hydrogen and water in condensed matter physics" 2009年10月 Chiba, Japan
  • Formation of compact amorphous H2O ice by a reaction of hydrogen atoms with oxygen molecules at low temperatures  [通常講演]
    Y. Oba, N. Miyauchi, T. Chigai, H. Hidaka, N. Watanabe, A. Kouchi
    Gordon Research Conferences, Matrix-Isolated Species, Physics & Chemistry Of 2009年07月 Magdalen College, Oxford, UK
  • Formation of interstellar ice by low temperature surface atomic reactions  [通常講演]
    A. Kouchi, Y. Oba, N. Miyahchi, H. Hidaka, N. Watanabe
    CRYO2009 2009年07月 Sapporo,Hokkaido,Japan
  • Effective formation of H2O by the H-addition to solid O2 on amorphous D2O ice  [通常講演]
    Y. Oba, N. Miyauchi, T. Chigai, H. Hidaka, N. Watanabe, A. Kouchi
    Workshop on Interstellar Matter 2008 2008年09月 Sapporo, Hokkaido,Japan
  • Incorporation of hydrous oxygen into insoluble organic matter (IOM) of Murchison  [通常講演]
    Y. Oba, H. Naraoka
    71th Annual Meeting of the Meteoritical Society 2008年07月 Matsue, Shimane,Japan
  • Isotopic variation of macromolecular organic matter from CM chondrites during hydrous pyrolysis  [通常講演]
    Y. Oba, H. Naraoka
    31th Symposium on Antarctic Meteorites 2007年06月 Tokyo, Japan
  • Carbon and hydrogen isotopic fractionations of organic compounds during UV degradation  [通常講演]
    Y. Oba, H. Naraoka
    16th Annual V. M. Goldschmidt Conference 2006年08月 Melbourne, Australia
  • Intramolecular carbon isotopic distribution of macromolecular organic matter in carbonaceous chondrites (CM)  [通常講演]
    Y. Oba, H. Naraoka
    68th Annual Meeting of the Meteoritical Society 2005年09月 Gatlinburg, TN, USA
  • Carbon and hydrogen isotopic compositions of acetic acid derived from macromolecular organic matter in the Murchison  [通常講演]
    Y. Oba, H. Naraoka
    29th Symposium on Antarctic Meteorites 2005年06月 Tokyo, Japan
  • A different behavior of hydrogen isotope exchange between two PAH isomers (fluoranthen and pyrene)  [通常講演]
    Y. Oba, H. Naraoka
    13th Annual V. M. Goldschmidt Conference 2003年09月 Kurashiki, Okayama, Japan

その他活動・業績

受賞

  • 2017年12月 地球化学研究協会 地球化学研究協会学術賞「進歩賞」
     新しい実験手法による安定同位体比を使用した炭素質隕石中の有機物と模擬星間分子の研究 
    受賞者: 大場康弘
  • 2010年 日本有機地球化学会 2010年度日本有機地球化学会研究奨励賞(田口賞)「
     炭素質隕石中有機化合物の安定同位体組成とその同位体分別プロセスに関する研究 
    受賞者: 大場康弘

共同研究・競争的資金等の研究課題

  • 原始地球上での核酸合成に関する新展開:地球外からの材料供給の可能性に迫る
    日本学術振興会:科学研究費助成事業 基盤研究(A)
    研究期間 : 2021年04月 -2025年03月 
    代表者 : 大場 康弘, 高野 淑識
  • 宇宙における未知の分子進化プロセスの探求:可視光による光化学反応
    日本学術振興会:科学研究費助成事業 挑戦的研究(萌芽)
    研究期間 : 2021年07月 -2023年03月 
    代表者 : 大場 康弘
  • 日本学術振興会:科学研究費助成事業 特別推進研究
    研究期間 : 2017年04月 -2022年03月 
    代表者 : 渡部 直樹, 大場 康弘, 杉本 敏樹, 中井 陽一
     
    超高真空実験槽中に氷星間塵表面を擬似したアモルファス氷表面を作製し,紫外線照射で生成したのOHラジカルの表面拡散の活性化エネルギーを求めることに,世界で初めて成功した(渡部,宮崎,羽馬)。また,OHラジカルの吸着状態と脱離メカニズムを明らかにした。これらの成果には,新たに雇用した研究補助者(WMC Sameera)の量子化学計算によるところが大きい。この結果を発表すべく,論文の執筆を始めた。 星間塵表面物質のひとつである炭素質表面を,グラファイトディスクのレーザーアブレーションにより真空実験槽内でその場作製し,その構造と作製条件の依存性を,透過型電子顕微鏡を用いて調べ,いつでも最適な試料表面を作製するノウハウを確立した(柘植,木村)。 極低温超高真空原子間力顕微鏡の特性を調べた。観測する基板が9~10Kの極低温に到達すること,それを維持出来る熱負荷の確認を行った。極低温下でシリコン結晶を観測することができ基本的な運転を習熟した。(日高,香内)。 氷表面上に分子イオンが吸着した際の生成物を検出するイオンピックアップ装置の立ち上げを行った。冷凍基板および赤外分光計,イオン源を超高真空槽に設置し,極低温氷の作製など予備実験を行った(渡部,大場,中井) 杉本は京都大学から分子科学研究所への異動に伴い,装置の移設・再構築を行った。また,分光測定中の振動ノイズを軽減するため,希釈冷凍機から液体ヘリウム貯め込み式の冷却方式への転換作業を進めた。氷表面に対する和周波発生振動分光を行ったところ,表面特有の水素結合構造を有する液晶相が熱力学的な安定相として氷表面に存在することを発見した。
  • 星間分子から隕石有機物へ:重水素存在度を指標とした分子進化プロセス解明
    若手研究(A)
    研究期間 : 2017年04月 -2021年03月 
    代表者 : 大場康弘
  • 星間分子雲初期に起こるケイ酸塩星間塵表面での分子進化
    日本学術振興会:科学研究費助成事業 基盤研究(A)
    研究期間 : 2017年04月 -2018年03月 
    代表者 : 渡部 直樹, 大場 康弘
     
    本研究は,未解明になっている,星間塵表面に氷マントルが生成される以前の,ケイ酸塩星間塵表面での分子生成,重水素濃集に着目し,化学・物理素過程を系統的かつ定量的な実験で調べ,星間塵上での分子進化の解明を目指すものである。採択と同時に,研究の根幹をなす,新たなケイ酸塩試料作製装置開発に向け,真空ポンプ,真空部品などを購入した。また,表面を原子間力顕微鏡で評価するため,カンチレバーチップを購入した。同時に,プラズマ放電による鉱物サンプル試料の作製を業者に依頼した。ケイ酸塩試料作製装置の開発は引き続き行っているところだが,業者に作製を依頼したサンプル試料がかなり高品質であることが分かった。 また,採択直後に東京理科大学にて,本研究課題についての研究討論を行い,本課題の独創性や重要性をアピールすることができた。 その後,すぐに現在実施中の特別推進研究が採択されたため,本研究課題の実施は7月28日をもって終了した。しかし,上記の取り組みは特別推進研究に引き継がれるため,基盤研究Aで行った討論,整備した装置類は将来にわたって有効に活用される。
  • 光化学反応による星間分子の重水素濃集度の変化
    新学術領域研究(研究領域提案型:公募研究)
    研究期間 : 2016年04月 -2018年03月 
    代表者 : 大場康弘
  • 日本学術振興会:科学研究費助成事業 基盤研究(S)
    研究期間 : 2012年05月 -2017年03月 
    代表者 : 渡部 直樹, 日高 宏, 大場 康弘, 羽馬 哲也, 香内 晃
     
    星間分子雲における分子生成・進化・同位体分別(化学進化)を明らかにすることは、太陽系の物質起源を研究するうえで重要である。本研究では、化学進化の鍵を握る、極低温下における氷星間塵表面でのトンネル反応による分子生成・重水素濃集プロセスを定量的な実験で調べた。氷表面での水素原子拡散係数と拡散メカニズム、水分子などの基本分子や始原的有機分子の生成・重水素濃集の反応経路やと化学進化に果たす役割を明らかにした。
  • 星間分子雲における硫黄の化学進化
    若手研究(A)
    研究期間 : 2014年04月 -2017年03月 
    代表者 : 大場康弘
  • 日本学術振興会:科学研究費助成事業 基盤研究(A)
    研究期間 : 2013年10月 -2016年03月 
    代表者 : 香内 晃, 日高 宏, 大場 康弘, 羽馬 哲也, 千貝 健, 渡部 直樹, 木村 勇気, 都丸 隆行
     
    氷の構造(ミクロ~マクロ)を解析するための超高真空極低温透過型電子顕微鏡を開発した.鏡体内で制御された条件での氷の作製が可能であり,氷に紫外線を照射することもできる. 本装置を用いて以下の研究を行った.(1)アモルファス氷のミクロな欠陥構造を初めて直接観察した.(2)氷Ih,氷Icへ75-100Kで紫外線を照射することにより,氷XIが生成されることを発見した.一方,アモルファス氷では相転移は観察されなかった.(3)CO:H2O=10:1-50:1を10Kで蒸着しその後温度を上昇させCOを昇華させると,高密度アモルファス氷が生成されることを見出した.この方法をマトリックス昇華法と命名した.
  • 星間塵表面反応による有機分子の重水素濃集:炭素鎖伸長による濃集度の変化
    新学術領域研究(研究領域提案型:公募研究)
    研究期間 : 2014年04月 -2016年03月 
    代表者 : 大場康弘
  • 日本学術振興会:科学研究費助成事業 研究活動スタート支援
    研究期間 : 2012年08月 -2014年03月 
    代表者 : 大場 康弘
     
    本研究では,星間分子雲における化学進化で重要な役割を担う星間塵表面反応による,アミノ酸の重水素濃集に関する研究をおこなった。もっとも単純なアミノ酸であるグリシンを超高真空反応チャンバー内に設置した反応基板(12K)に蒸着し,重水素原子と反応させた。FTIRやNMRで反応生成物を分析したところ,グリシンの重水素置換体の生成が確認された。反応には高い活性化エネルギーが存在するため,極低温での重水素置換体生成には量子力学的なトンネル効果が重要だと考えられる。本研究では,アミノ酸が星間分子雲における極低温表面原子反応によって重水素濃集可能であることを示した。
  • 星間分子雲における極低温表面原子反応によるアミノ酸の重水素農集機構の解明
    研究活動スタート支援
    研究期間 : 2012年08月 -2014年03月 
    代表者 : 大場康弘
  • 極低温星間塵表面原子反応によるアミノ酸の生成機構
    日本学術振興会:科学研究費助成事業 特別研究員奨励費
    研究期間 : 2009年 -2011年 
    代表者 : 大場 康弘
     
    メチルアミンの部分重水素置換体,CH_3ND_2およびCD_3NH_2を用いて,それぞれをH原子およびD原子と反応させ,各置換基のH-DおよびD-H交換速度を求めた。メチルアミンのメチル基のH-D交換,D-H交換,そしてアミノ基のH-D交換,D-H交換速度定数をそれぞれRc_,Rc_,Rn_,Rn_とすると,Rc_D > Rc_ >> Rn_ > Rn_という関係が得られた。同じ置換基のH-DおよびD-H交換速度を比較すると,H-D交換,つまりD濃縮反応のほうが速いことが明らかになった。また,CH_3NH_2全体のH-D交換反応,およびCD_3ND_2全体のD-H交換反応の速度定数をそれぞれR_,R_,とすると,R_〓Rc_,R_〓Rc_という関係が成立した。これはメチル基の水素交換速度がメチルアミン全体の水素交換速度を支配していることを意味する。これは,メチル基・アミノ基の水素交換が同時に起きているためだといえる。 メチルアミンのD(H)濃縮反応は,D(H)原子によるH(D)引き抜き反応→D(H)原子付加反応によって進行すると考えられる。たとえば(1)CH_3NH_2 + D→CH_2NH_2 + HD,(2)CH_2NH_2 + D→CH_2DNH_2のように進む。反応(2)はラジカル同士の反応であるため,速やかに進む。一方,反応(1)には分子からH(D)原子を引き抜く際に,2000-5000Kというエネルギー障壁が存在する。~10Kという極低温では反応(1)に必要なエネルギーを得ることは難しく,熱的に反応は進行しない。したがって,反応(1)は量子的なトンネル効果によって進行したと結論できる。 本研究で,メチルアミンは水素同位体交換しやすい分子であることがわかった。これは,星間分子雲の重水素濃集モデルで見積もられている最大のD/H原子比(~0.05)と,R_R_の比(R_/R_たとえば~2at 10K)を考慮すると,星間分子雲でのメチルアミンは水素交換反応によってそのD/H比が10^<-2>オーダーであることを示唆する。これは,星間分子雲に存在するメタノールやホルムアルデヒドの高いD/H比(~10^<-2>-10^<-1>)に匹敵する。いまだメチルアミンの重水素置換体の存在は星間空間で確認されていないが,今後の発見が期待される。
  • 地球外有機分子の多次元同位体組成解析による化学進化メカニズムの解明
    日本学術振興会:科学研究費助成事業 特別研究員奨励費
    研究期間 : 2005年 -2006年 
    代表者 : 大場 康弘
     
    低分子有機化合物(酢酸、プロピオン酸、メタノール、アセトニトリル、ベンゼン、アセトン)に高圧水銀ランプから発せられる紫外線を照射し、その分解に伴う炭素・水素同位体分別を明らかにした。各化合物は紫外線照射時間とともに分解が進み、アセトンが最も早く分解した。また、酢酸とプロピオン酸もアセトンについで分解が早かった。これら3種類の化合物はその構造に炭素-酸素二重結合(カルボニル基)をもつことから、カルボニル基は本研究で用いた紫外線をより効率よく吸収することが示された。各化合物の半減期は17から550分であった。 各化合物は分解とともに炭素・水素同位体比ともに大きくなった。炭素同位体分別係数は0.9968から0.9875、水素同位体分別係数は0.9890から0.9406であった。分解速度の順序と炭素・水素同位体分別係数の大きさの順序には相関は見られず、化学的に安定な化合物が同位体的に安定であるというわけではないことが明らかになった。 分解に伴う同位体分別の大きさの順序が炭素、水素でまったく異なった。これは同位体分別のメカニズムが炭素と水素でまったく異なることを示唆する。例えば水素同位体分別の場合は、水素ラジカルなどの化学的に活性種が紫外線照射により生成し、それが化合物と反応することで分解・同位体比変化が起こるというメカニズムが想定されるが、炭素同位体分別の場合には考えにくい。したがって、分解のされやすさだけでなく、化学的に活性な分子種の種類や量にも同位体比変化は依存している可能性がある。 このように有機化合物の紫外線分解は、宇宙空間や地球大気中など紫外線に富む環境では有機化合物の同位体組成に影響を及ぼすひとつの要因となりうることが示された。
  • 星間塵表面原子反応によるアミノ酸前駆物質の生成機構
    若手研究(B)
    代表者 : 大場康弘

教育活動情報

主要な担当授業

  • 宇宙低温物質科学特論
    開講年度 : 2021年
    課程区分 : 修士課程
    開講学部 : 理学院
    キーワード : 星間分子雲,彗星,化学進化,ダスト、核生成、結晶成長、地球外有機物,生命の起源、電子顕微鏡、ナノ粒子


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